Bubble Charts

A Bubble chart is a graphical representation of 3-dimensional data in the form of disks. The disks represent each element with its associated triplet (v1, v2, v3). Its triplet consists of its 2 values that are expressed through the coordinates of the disk, and its third value which is represented by the size of the disk. They are often employed in explaining scientific relationships, e.g., medical, social, and economical. They could be considered a variant of scatter plots.

Bubble charts suffer from issues related to clarity and accuracy. Human biology receives the image of a disk in terms of its area, which is proportional to the square of the radius; consequently, if the disks are scaled to the 3rd data value directly, the differences in disk size will be misleading. The radius of each disk must be scaled to the square root of the corresponding v3. In datasets with a large spread, it is possible for this scaling problem to cause significant misinterpretations. Many people are unaware of this issue or ignore it, so many are hesitant to utilize bubble charts because they question their accuracy. This issue is solved by some users by properly labeling bubble charts to indicate that they have been designed to convey information with area. Another negative of bubble charts is that they cannot logically represent zero or negative values. A solution for this problem is to use symbols, color-coding, or other shapes.

The scope of information that bubble charts can convey is rather limited. Some attempt to solve this problem by using graphic characteristics creatively. They use specific patterns, shading, and other information to express more information. This can work in some cases, however, it can also result in overload, which is the opposite of a graph's purpose.

Bubble charts are also limited in scope by their volume limitations because they cannot present more than a specific amount of bubbles, or they become problematic to interpret. It can be argued that even a simple bubble chart suffers from overload, because unlike other charts, it (usually) does not offer the user the ability to quickly interpret its information. Its information simply is not presented in a clear and direct way.